The handling of exogenous materials by the rat parotid gland is under investigation. Tracers of various molecular weights are presented to the luminal surface of the acinar cells by retrograde injection through the duct, or to the basal and lateral surfaces by intravenous or interstitial injections. The uptake of material and its subsequent utilization in stimulated and unstimulated cells is being followed by light and electron microscopy. Attention is focused on the role of the Golgi complex and lysosomes in the disposition of this material, and on its possible incorporation into secretory granules. Additionally, membrane flow is being studied by use of retrograde injections.